Study of phase formulation in CrN thin films and its response to a minuscule oxygen flow in reactive sputtering process

Abstract We studied CrN thin films grown by a reactive direct current magnetron sputtering process. Starting with pure Cr, as nitrogen is added, initially N atoms occupy interstitial positions in bcc Cr and when the amount of N increases an amorphous structure emerge. Subsequently, fcc chromium mononitride (CrN) phase start to appear and stoichiometric CrN get formed when the amount of reactive nitrogen gas is about one-third of argon gas. While, the long range ordering of CrN film seems to be stable up to 873 K, signatures of local instabilities can be seen in the N K-edge absorption pattern at lower temperatures. To improve the thermal stability of CrN films, we used oxygen (O) as a surfactant. We found that O works like a surfactant when used in a minuscule amount (0.25%). In the O surfactant mediated growth, O does not react with CrN film. An accumulation of O at the surface of CrN film can be seen in the O K-edge absorption pattern, typically expected in surfactant mediated growth. However, when the amount of O gas flow is increased from 0.25 to 0.5%, it no longer acts as a surfactant and severely affects both long and short range structure of CrN film as occurrence of Cr2O3 phase can now be seen. Surfactant mediated CrN films clearly show denser and smoother films with superior thermal stability.